The goal of this proposal is to further develop our magneto-endosymbiont (ME) technology for in vivo single cell MRI detection (Phase 1) and functional reporting (Phase 2) thus creating a robust translational tool for cell based research. MEs were derived from magnetic bacteria creating a living contrast agent that enables in vivo cell tracking. MRI is a highly translatable technique for visualizing implanted cells because it is non- invasive and provides extremely high anatomical resolution. MEs are a unique contrast agent because they have a large genetic capacity that can be leveraged to encode functional reporters, in vivo. The effectiveness of MEs for single cell tracking will be experimentally assessed in a metastatic brain cancer model, that we have previously used to demonstrate single cell MRI tracking with superparamagnetic iron oxide particles. Tools that provide insight into detailed cellular events at the single cell level in situ will advance oncology research, regenerative medicine research, personalized diagnostics and the clinical realization of cell therapies.